[Feat] r.proj should preserve input map metadata

[marisn]

r.proj writes only history of its call, but nothing about input map. Still reprojected map is (almost) the same map, only with a different coordinate system. Thus r.proj should copy over most of input map metadata.

Implementing copy is easy (I do have ready code), but there also has to be implemented new functions in the raster library, as history and other metadata reading functions do not support reading from a different project (location). Thus closing this bug will take two separate PRs.

[sakirr05]

hey @marisn @petrasovaa Can you please tell which metadata fields it’s expected to preserve? Should it include custom key/value categories, category labels, temporal meta? or Do you expect full metadata echo or only specific parts?

[marisn]

r.proj should mirror all of metadata, colour tables etc. Only difference should be an extra history entry indicating r.proj run (and, of course new projection/resolution etc). As I wrote, it needs a thoughtful approach as it requires a bunch of new core library functions that do accept project (location) as an extra parameter for element search and read. Thoughtful to understand if r.proj should read those files directly bypassing core library or core library should be extended and how that extension should be implemented.